Gear reducer comprising a worm and a crown-wheel assembly provided with a torque limiter

ABSTRACT

A gear reducer comprising a worm and a crown-wheel assembly, in turn comprising a crown wheel, which is connected/disconnected to/from a drive shaft by means of a torque limiter mounted on this latter. The gear reducer is characterised in that the drive shaft and the torque limiter are comprised in a cartridge which can be extracted/inserted from/in a cavity obtained in the crown-wheel assembly according to an axial direction and in accordance with two opposite senses, without the need to disassemble the worm.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application is a U.S. national stage application under 35U.S.C. §371 of PCT Application No. PCT/IB2013/051570, filed Feb. 27,2013, which claims priority to Italian Application No. BO2012A000090filed Feb. 27, 2012, the entireties of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a gear reducer comprising a worm and acrown-wheel assembly provided with a torque limiter.

BACKGROUND ART

A gear reducer of this type is known from the European patentapplication EP-A1-1 793 143 filed by the present applicant.

One of the main defects of the gear reducer described in this documentis constituted by the fact that it is difficult to disassemble. In fact,for example, in the case in which it is necessary to change a worn discof the torque limiter, the crown-wheel assembly must first bedisassembled from the worm to allow extraction of the whole crown-wheelassembly.

DISCLOSURE OF INVENTION

The aim of the present invention is to provide a simple and reliablesolution to the problem of disassembly of the torque limiter withoutrequiring to disassemble the whole gear reducer.

Therefore, the present invention relates to a gear reducer comprising aworm and a crown-wheel assembly, in turn comprising a crown wheel, whichis connected/disconnected to/from a drive shaft by means of a torquelimiter mounted on this latter; the gear reducer is characterised inthat the drive shaft and the torque limiter are comprised in a cartridgewhich can be extracted/inserted from/in a cavity obtained in thecrown-wheel assembly according to an axial direction and in accordancewith two opposite senses, without the need to disassemble the worm.

BRIEF DESCRIPTION OF THE DRAWINGS

The example below is provided purely for non-limiting illustrativepurposes, to allow better understanding of the invention with the aid ofthe accompanying figures, wherein:

FIG. 1 shows a longitudinal section A-A of a preferred embodiment of aworm/crown-wheel-assembly gear reducer forming the main object of thepresent invention;

FIG. 2 shows a cross section B-B of the gear reducer of FIG. 1; and

FIG. 3 shows a partially exploded view of the gear reducer of FIGS. 1and 2.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1 the worm/crown-wheel-assembly gear reducer forming the mainobject of the present invention has been indicated as a whole with thereference number 1.

The gear reducer 1 is suited to transmit a rotary motion between twomutually orthogonal axes 2 and 3 (each of which identifies a respectiveaxial direction) and comprises a worm fitted on a shaft 5 coaxial withthe axis 2, and a crown-wheel assembly 6 suited to rotate about the axis3. The worm 4 and the crown-wheel assembly 6 are contained within acasing 7.

In turn, the crown-wheel assembly 6 comprises a crown wheel 8, acrown-wheel-carrier hub 9 and a drive shaft 10 supported by the samecrown-wheel-carrier hub 9.

It must be noted that the crown wheel 8, the crown-wheel-carrier hub 9and the drive shaft 10 have the same axis 3 as longitudinal axis ofsymmetry. Moreover, the drive shaft 10 is inserted inside a cavity 100obtained in the crown-wheel-carrier hub 9. It must also be noted that aportion 10A of the surface of the drive shaft 10 is coupled withoutinterference with the portion 100A of the crown-wheel-carrier hub 9.

As well known in the art, the crown wheel 8, normally made of bronze, iscast directly onto the crown-wheel-carrier hub 9, normally made of castiron, so that the two elements are integral with each other.

The crown-wheel assembly 6 also comprises a torque limiter 11, which, aswill be better explained below, is suited to make thecrown-wheel-carrier hub 9 (and, therefore, also the crown wheel 8 which,as already stated, is integral with this crown-wheel-carrier hub 9), andthe drive shaft 10 integral with each other.

More in detail, the torque limiter 11 comprises an assembly of discs 12composed of a first group of discs 12A made of a material with highfriction coefficient, in use, mechanically coupled to thecrown-wheel-carrier hub 9, alternated with a second group of discs 12Bmade of steel, in use mechanically coupled to the drive shaft 10. Whenthe assembly of discs is in its packed configuration, the rotary motionabout the axis of the crown wheel 8 is transmitted first to thecrown-wheel-carrier hub 9 (integral with the crown wheel 8) and then tothe drive shaft, due to the two groups of discs 12A, 12B packed againsteach other (see below).

By observing FIG. 2 it can be noted that each disk 12A is provided witha series of outer projections 12A* equidistant from one another. Eachouter projection 12A* is inserted in a respective longitudinal seat 9A*obtained on the surface of the cavity 100, which, as stated, is obtainedin the crown-wheel-carrier hub 9.

Analogously, each disc 12B is provided with a plurality of innerprojections 12B*, which are coupled with longitudinal seats 10A*obtained on the outer surface 10D of the drive shaft 10.

In actual fact, in FIG. 2 any disc 12B, coupled with the drive shaft 10,is covered, almost totally, by a respective disc 12A, placed in front ofthe disc 12B, coupled with the crown-wheel-carrier hub 9.

Therefore, in FIG. 2 only the inner projections 12B* of the disc 12B arevisible, each of which, as stated previously, is inserted in arespective seat 10A* obtained on the outer surface 10D of the driveshaft 10.

As is well known in the art, if the torque transmitted between the worm4 and the crown wheel 8 by means of the gear reducer 1 exceeds a certainpredetermined value, the first group of discs 12A of the torque limiter11 slips with respect to the second group of discs 12B according to thedescription provided, for example, in the aforesaid European patentapplication EP-A1-1 793 143.

As shown in FIG. 1, the shaft 10 contains a stop 10E extending radiallywith respect to the axis 3, and against which the assembly of discs 12is thrust under the action of a spacer 13 compressed by a pair ofBelleville washers 14 (with axis 3) arranged around the drive shaft 10.

Moreover, the torque limiter 11 comprises a safety and adjusting washer15, also arranged around the drive shaft 10; this safety washer 15 isalso subjected to the action of the Belleville washers 14 and held inposition by a locking ring nut 16 screwed onto the drive shaft 10provided on its surface with a thread 10B.

In other words, the axial position of the adjusting and locking ring nut16, and therefore also of the safety washer 15, through the spacer 32,determines the extent of compression of the Belleville washers 14, whichexert a thrust on the spacer 13 which, in turn compacts the assembly ofdiscs 12 against the aforesaid opposing stop 10E.

The torque limiter 11 is closed inside the casing 7 by a lid 17 screwedonto the same casing 7 by means of a plurality of screws 18 (FIG. 1). Onthis lid 17A a longitudinal seat 19 is obtained (centred on the axis 3),which houses a rolling bearing 20 with axis 3 into which, in use, an end10C of the drive shaft 10 is inserted. This centring bearing 20 enablesperfect centring of the drive shaft 10 with respect to the axis 3.

By going back to the crown-wheel-carrier hub 9, it can be noted that ithas a substantially cylindrical shape and that it is provided with twolateral shoulders 9C and 9D, each of which is suited to house arespective rolling bearing 21, 22 onto which the stresses on thecrown-wheel assembly 6 are discharged.

The rolling bearing 21, on one side, is housed in the shoulder 9Cobtained on the outer surface of the crown-wheel-carrier hub 9, whereas,on the other side, it is housed in a breaking 23 obtained in a body 24.

Analogously, the rolling bearing 22, on one side, is housed in theshoulder 9D obtained on the outer surface of the crown-wheel-carrier hub9, whereas, on the other side, it is housed in a breaking 25 obtained ina closing element 26 (FIG. 1), which is screwed to the casing 7, towhich the lid 17 is effectively screwed.

As shown in FIGS. 1, 3, the crown-wheel-carrier hub 9 has a number ofradial holes 30 to allow the passage of lubricating oil from an areaoccupied by the worm 4 and by the crown wheel 8 to an area in which thetorque limiter 11 is housed.

Moreover, it can be noted that, as shown in FIG. 2, the distance (D1)between the bottoms of two diametrically opposite longitudinal seats 9A*is greater than the distance (D2) between the crests of twodiametrically opposite outer projections 12A*.

In fact, if we name the assembly given by the drive shaft 10 and by theassembly of discs 12 of the torque limiter 11 “cartridge 200”, it can benoted that, due to the fact that the distance (D1) is greater than thedistance (D2), this cartridge 200 can be easily extracted from the gearreducer 1 simply by unscrewing the lid 17 (FIG. 3) and removing thiscartridge 200 axially from the cavity according to a sense given by anarrow (F1).

In other words, the fact that the distance (Dl) is greater than thedistance (D2) ensures that the cartridge 200 can be extracted from thecavity 100 (according to the arrow (F1); FIG. 3) simply by sliding itout, without any interference whatsoever between any portion of thecartridge 200 and the remaining elements of the gear reducer 1.

During the operation to remove the cartridge 200 (according to the arrow(F1)), each outer projection 12A* slides axially in the respectivelongitudinal seat 9A* (FIG. 3).

Incidentally, it must be noted that the following elements can also bemounted on the shaft 10:

-   -   the spacer 13;    -   the pair of Belleville washers 14;    -   the safety washer 15;    -   the spacer 32; and    -   the adjusting and locking ring nut 16.

Therefore, by extracting the cartridge 200 from the cavity 100 theaforesaid elements 13, 14, 15, 32, 16 can also be removedsimultaneously.

During maintenance of the gear reducer 1, after having changed anydamaged elements of the cartridge, the operator inserts the overhauledcartridge 200 into the cavity 100 according to a sense given by thearrow (F2) opposite that of the aforesaid arrow (F1).

Naturally, in this reverse operation each outer projection 12A* slidesaxially in the respective longitudinal seat 9A* according to the arrow(F2) (FIG. 3).

Given that the aforesaid elements 13, 14, 15, 32, 16 have already beenmounted on the shaft 10, after having adjusted the thrust force, bymeans of the adjusting and locking ring nut 16, exerted on the discs 12by the pair of Belleville washers 14, the operator closes the lid 17,screwing down the screws 18 on the closing element 26.

The main advantage of the gear reducer forming the subject of thepresent invention consists in the fact that it facilitates disassemblyof the torque limiter and of the shaft that supports it withoutrequiring to disassemble the rest of the gear reducer.

A further advantage is given by the fact that, due to the centringbearing on the lid, centring of the shaft with the longitudinal axis ofsymmetry of the gear reducer is obtained.

1. A gear reducer comprising: a worm; and a crown-wheel assembly, thecrown-wheel assembly comprising a crown wheel, which isconnected/disconnected to/from a drive shaft by means of a torquelimiter mounted on this latter; wherein said drive shaft and said torquelimiter are comprised in a cartridge which can be extracted/insertedfrom/in a cavity obtained in said crown-wheel assembly according to anaxial direction and in accordance with two opposite senses, without theneed to disassemble said worm.
 2. The gear reducer as claimed in claim1, wherein said cavity is provided with a plurality of longitudinalseats, each of which is suited to house a respective outer projection ofa related disc belonging to said torque limiter.
 3. The gear reducer asclaimed in claim 1, wherein the outer surface of said drive shaft isprovided with a plurality of longitudinal seats each of which is suitedto house a respective inner projection of a related disc belonging tosaid torque limiter.
 4. The gear reducer as claimed in claim 1, whereinthe following elements are mounted on said drive shaft: a first spacer;a pair of Belleville washers; a safety washer; a second spacer; and anadjusting and locking ring nut.
 5. The gear reducer as claimed in claim1, wherein said cavity is closed by a lid having a longitudinal seatsuited to house in its inside centring means, into which an end of saiddrive shaft is inserted.
 6. The gear reducer as claimed in claim 2,wherein the distance between the bottoms of two diametrically oppositelongitudinal seats is greater than the distance between the crests oftwo diametrically opposite outer projections.
 7. The gear reducer asclaimed in claim 1, wherein between said crown wheel and said driveshaft there is interposed a crown-wheel-carrier, on which said crownwheel is fitted, said crown-wheel-carrier hub being separate from saiddrive shaft and being supported by respective support means, which areindependent of said drive shaft.
 8. The gear reducer as claimed in claim7, wherein the gear reducer is provided with a first rolling bearing,which, on one side, is housed in a shoulder obtained on the outersurface of said crown-wheel-carrier hub, whereas, on the other side, itis housed in a breaking obtained in a body.
 9. The gear reducer asclaimed in claim 7, wherein the gear reducer is provided with a secondrolling bearing, which, on one side, is housed in a shoulder obtained onthe outer surface of said crown-wheel-carrier hub, whereas, on the otherside, it is housed in a breaking obtained in a closing element.
 10. Thegear reducer as claimed in claim 7, wherein the gear reducer is providedwith a plurality of radial holes, suited to allow the passage of alubricating oil from an area occupied by the worm to an area in whichthe torque limiter is housed.